1. Field of the Invention
The present invention relates to a liquid crystal display element, and particularly relates to a liquid crystal display element containing a liquid crystal component exhibiting a cholesteric phase at room temperature.
2. Description of the Related Art
A liquid crystal display (LCD) element is basically composed of a pair of substrates having transparent electrodes and a liquid crystal layer provided between the substrates. The arrangement of liquid crystal molecules is controlled by application of a predetermined driving voltage to the liquid crystal layer, so that external light incident to the liquid crystal element is modulated. By so doing, intended image display, and the like, is carried out. In some cases, the LCD element may include space maintaining members between the substrates so that a space between the substrates is maintained.
Various types of such LCD elements have been proposed, and recently studied are various types of LCD elements utilizing chiral nematic liquid crystal to which a chiral material is added so as to exhibit a cholesteric phase at room temperature.
Such an LCD element is sometimes used as, for instance, a reflective LCD element utilizing the selective reflection function of chiral nematic liquid crystal in some cases. In this reflective LCD element, for display, the state of liquid crystal is switched between a planer state (colored state obtained by selectively reflecting visible light with specific wavelengths) and a focal conic state (transparent state) in response to application of high and low pulse voltages. Further, a region in the planer state remains in the planer state while a region in the focal conic state remains in the focal conic state even after pulse voltage application (this maintenance of the respective planer and focal conic states is generally referred to as bistability or memory effect) and (with this bistability or memory effect) it is possible to maintain the obtained display even after voltage application is stopped.
Furthermore, as a method for realizing full-color display with an LCD element of this type, a method is taken as an example that utilizes a multi-layer LCD element having three layers, namely, a red (R) liquid crystal layer for red color display, a green (G) liquid crystal layer for green color display, and a blue (B) liquid crystal layer for blue color display is taken as an example.
As to an LCD element having, between a pair of substrates, a liquid crystal layer containing chiral nematic liquid crystal, the driving of the same has required application of a driving voltage of around 60 V in the prior art, and hence, an LCD device that is driven with a lower driving voltage is demanded. It is particularly necessary to provide an LCD element that is driven with a driving voltage of not higher than about 40 V so that an inexpensive universal driving IC is used as the driving IC for driving the LCD element.
To drive the LCD element at a lower voltage, the liquid crystal layer may be formed thinner. This, however, causes the light reflectance to decrease, thereby darkening image display and hence deteriorating contrast.